UCC256301: UCC256301 not stable and shut down

Dear Team,

My customer use PMP20795 as their reference for design.

I have to say, the design is almost the same.

Same transformer, resonant inductor and so on.

But the waveform of the resonant current is quite weird. The out put voltage is quite stable at 24V for a while before shut down.

I think is because the system is not stable. If I want to reduce the feedback bandwidth to stable the circuit, how to do it?(don't care about the transient response)

Ch1: low side Vgs, Ch2:Iresonant

Ch1: Vo, Ch2:Iresonant

Thanks a lot

Best Regards

Kevin